Is female sexuality more fluid than male sexuality?

Or is it little more than social condition that makes it seem that way to me?

I know far more women who would be happy to kiss another woman, or even to have sex with one, than I know men who'd kiss another man. And most of the men that I know who would do it aren't that keen on kissing women. Does this mean that more women are somewhat bi-sexual than men, or are they just less inhibited? Or is the whole thing merely social conditioning?

Thanks for your thoughts!
Gwennie B: Thanks for the book recommendation - I will look that one up.